Variable valve operating system for internal combustion engine

ABSTRACT

A variable valve operating system includes a position changing mechanism, which is configured by a circular eccentric portion provided for a control shaft of a engine valve in a manner decentered from an axis of the control shaft, an external gear formed on a cam follower swingably supported on the eccentric shaft portion, and an internal gear formed on a rocking cam so as to be engaged with the external gear. The control shaft is rotated when opening/closing characteristics of the engine valve are changed, the external gear is revolved by the eccentric shaft portion around the axis of the control shaft, an engaged portion of the internal gear with the external gear is moved in a circumferential direction of the internal gear by the revolution of the external gear, and the position of the rocking cam with respect to the cam follower is changed by the movement of the engaged portion of the internal gear.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable valve operating system foran internal combustion engine, and more particularly, to a variablevalve operating system for an internal combustion engine whichcontinuously changes lift characteristics of an engine valve.

2. Related Art

In a conventional art, in order to continuously change lift amount andoperating angle of an engine valve according to an operating state of aninternal combustion engine, there has been provided a vehicle internalcombustion engine including a variable valve operating system. Thevariable valve operating system swingably supports a rocking cam whichlifts the engine valve on a control shaft, couples a cam follower, whichis rocked by a rotating cam of a camshaft and rocks the rocking cam, tothe rocking cam through a position changing mechanism, and changes liftcharacteristics of the engine valve by changing a relative positionalrelationship of the rocking cam with respect to the cam follower by theposition changing mechanism.

According to the variable valve operating mechanism for internalcombustion engine and intake air amount control device disclosed inPatent Document 1 (Japanese Patent No. 3799944), for example, a relativephase difference between an input portion and an output portion of anintermediary drive mechanism is changed. That is, a phase differencebetween a rocker arm for inputting from a cam to a control shaftdifferent from a camshaft and a rocking cam for outputting to a rollerrocker arm is changed by engagement of a helical spline. At this time,axial movement of the control shaft achieves and realizes a change inengagement of the helical spline.

However, in a conventional structure such as disclosed in the abovePatent Document 1, the variable valve operating mechanism for theinternal combustion engine provides a matter to be solved such that thephase is controlled by the axial movement of the control shaft, andthus, an error in a valve lift between cylinders increases with thetemperature difference of the internal combustion engine. This isbecause the cylinder head is made of aluminum and the control shaft ismade of iron, both of which are components or parts of the variablevalve operating mechanism, so that the change in length due totemperature change differs between the cylinder head and the controlshaft.

Further, it is difficult to manufacture the helical spline, which maycause an increase in cost, thus being inconvenient and disadvantageous.

Furthermore, in the above configured variable valve operating system,although the valve lift amount is advantageously variable, the camtiming for operating the engine valve is fixed, which may likely causedisadvantageous matter in terms of performance.

SUMMARY OF THE INVENTION

The present invention was conceived in consideration of thecircumstances mentioned above and an object of the present invention isto provide a variable valve operating system for an internal combustionengine capable of eliminating variations in lift characteristics foreach engine valve due to the thermal expansion difference betweenstructural components or parts as well as improving manufacturability ofthe internal combustion engine.

The above and other objects can be achieved according to the presentinvention by providing, in one preferable aspect, a variable valveoperating system for an internal combustion engine including an enginevalve and a cam shaft operating the engine valve, the variable valveoperating system comprising:

a rocking cam, which lifts the engine valve, supported to a controlshaft to be swingable;

a cam follower rocking the rocking cam;

a position changing mechanism which couples the cam follower with therocking cam, the position changing mechanism being configured to changea relative positional relationship of the rocking cam with respect tothe cam follower to thereby change lift characteristics of the enginevalve,

the position changing mechanism comprising: a circular eccentric portionwhich is formed to the control shaft in a manner decentered from an axisof the control shaft; an external gear formed on the cam followerswingably supported on the eccentric shaft portion with the eccentricshaft portion as the rotating shaft; and an internal gear formed on therocking cam with the control shaft as the rotating shaft so as to beengaged with the external gear,

wherein the control shaft is rotated when opening/closingcharacteristics of the engine valve are changed, the external gear isrevolved by the eccentric shaft portion around the axis of the controlshaft, an engaged portion of the internal gear with the external gear ismoved in a circumferential direction of the internal gear by therevolution of the external gear, and the position of the rocking camwith respect to the cam follower is changed by the movement of theengaged portion of the internal gear.

In a preferred embodiment of the above aspect of the present invention,it may be desired that when the control shaft is rotated, the camfollower moves such that a contact point to the rotating cam moves alongan outer circumference of the rotating cam and the movement of therocking cam causes a lift amount of the engine valve to be changed, andwhen the control shaft is rotated in a direction to reduce the liftamount of the engine valve, the contact point between the cam followerand the rotating cam moves in a direction opposite to the rotatingdirection of the rotating cam.

It may be also desired that the rocking cam includes a base circleportion which prevents the engine valve from being lifted and a camportion which is projected radially from the base circle portion, ahollow portion is formed on an inner circumference of the base portion,the internal gear is formed on an inner circumference surface of thehollow portion, and the external gear and the eccentric shaft portionare arranged inside the hollow portion.

According to the present invention of the characters mentioned above, itbecomes possible to effectively eliminate variations in liftcharacteristics for each engine valve due to the thermal expansiondifference between parts and improve manufacturability, thus beingeffective and advantageous.

The nature and further characteristic features of the present inventionwill be made clearer from the following descriptions made with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a perspective view of a variable valve operating system for aninternal combustion engine according to an embodiment of the presentinvention;

FIG. 2 is an exploded view of the variable valve operating system forthe internal combustion engine according to the embodiment;

FIG. 3 is a sectional view of the variable valve operating system forthe internal combustion engine according to the embodiment, taken alongthe line in FIG. 1;

FIG. 4 illustrates an operation of an engine valve and includes FIG. 4Arepresenting an engine valve operation under small lift andnon-operating conditions, and FIG. 4B representing the engine valveoperation under small lift and operating conditions;

FIG. 5 illustrates an operation of an engine valve and includes FIG. 5Arepresenting an engine valve operation under large lift andnon-operating conditions, and FIG. 5B representing the engine valveoperation under large lift and operating conditions; and

FIG. 6 is a graph representing a relationship between a lift amount andan opening/closing timing of the engine valve according to theembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A variable valve operating system for an internal combustion engineaccording to a preferred embodiment of the present invention will bedescribed hereunder with reference to the accompanying drawings forachieving an object mentioned hereinbefore.

Further, it is to be noted that, in the following description withreference to the illustrated embodiment, a crank (crankshaft) axialdirection of an internal combustion engine 1 (FIG. 3) is called “afront-back (longitudinal) direction”, a cylinder axial direction iscalled “a vertical direction”, and a direction perpendicular to thecrank axial direction and cylinder axial direction is called “a lateraldirection”, and furthermore, it is also noted that terms “upper”,“lower”, “right”, “left” and the like terms are used herein withreference to the illustrated embodiment and in an actually arrangedstate of the internal combustion engine.

With reference to FIGS. 1 to 3, an internal combustion engine 1 includesan engine valve 2 having an intake valve and an exhaust valve foropening and closing an intake port and an exhaust port communicated witha combustion chamber of a cylinder head. As illustrated in FIG. 3, in afront view, the engine valve 2 has an axial line C inclined at apredetermined angle and supported on the cylinder head so as to bevertically movable.

The engine valve 2 includes one side engine valve 2A arranged on a frontside and the other side engine valve 2B arranged on a rear side, whichare arranged side by side one another.

The one side (front side) engine valve 2A includes one side (front side)valve head 3A having a distal end portion is detachably connected a portopening, and this one side valve stem 4A having a distal end sidecontinuously connected to the one side valve head 3A. The other side(rear side) engine valve 2B includes the other side (rear side) valvehead 3B having a distal end portion detachably connected to the portopening, and the other side valve stem 4B having a distal end sidecontinuously connected to the other side valve head 3B.

Further, the one side valve head 3A and the other side valve head 3Bconstitute a valve head 3, and the one side valve stem 4A and the otherside valve stem 4B constitute a valve stem 4.

The internal combustion engine 1 further includes a roller fingerfollower (RFF: rocker arm) 5 which opens and closes the engine valve 2in accordance with the axial (upward/downward) movement thereof.

The roller finger follower 5 includes one side roller finger follower 5Acorresponding to the one side engine valve 2A, and the other side rollerfinger follower 5B corresponding to the other side engine valve 2B.

The one side roller finger follower 5A includes: one side arm portion 6Aarranged so as to be oriented in a horizontal direction and a left/rightdirection, one side roller shaft 7A supported at a central portion ofthe one side arm portion 6A; one side roller 8A mounted to the one sideroller shaft 7A to be rotatable; one side valve abutting portion 9Aformed at a left end portion of the one side arm portion 6A; and oneside adjuster support portion 10A formed at a right end portion of theone side arm portion 6A. This one side adjuster support portion 10A issupported on a top spherical portion of one side hydraulic lash adjusterportion 11A.

In the like manner, the other side roller finger follower 5B includes:the other side arm portion 6B arranged so as to be oriented in ahorizontal direction and a left/right direction; one side roller shaft7B supported on a central portion of the other side arm portion 6B; theother side roller 8B mounted to the other side roller shaft 7B to berotatable; the other side valve abutting portion 9B formed at a left endportion of the other side arm portion 6B; and the other side adjustersupport portion 10B formed at a right end portion of the other side armportion 6B. This other side adjuster support portion 10B is supported ona top spherical portion of the other side hydraulic lash adjusterportion 11B.

In this illustrated structure, the one side arm portion 6A and the otherside arm portion 6B constitute an arm portion 6. The one side rollershaft 7A and the other side roller shaft 7B constitute a roller shaft 7.The one side roller 8A and the other side roller 8B constitute a roller8. The one side adjuster support portion 10A and the other side adjustersupport portion 10B constitute an adjuster support 10. The one sidehydraulic lash adjuster portion 11A and the other side hydraulic lashadjuster portion 11B constitute a hydraulic lash adjuster 11.

A camshaft 12 is arranged so as to be supported on the cylinder head ofthe internal combustion engine 1 in a forward-backward direction and tobe rotatable in synchronism with a crankshaft of the internal combustionengine 1 to thereby drive the engine valve 2.

A rotating cam 13 is integrally mounted on the camshaft 12, and therotating cam 13 includes a base circle portion 14 and a cam portion 15projected radially from the base circle portion 14.

The internal combustion engine 1 further includes a variable valveoperating system 16 which changes lift characteristics of the enginevalve 2.

As illustrated in FIGS. 1 to 3, the variable valve operating system 16includes a control shaft 17 arranged between the engine valve 2 and thecamshaft 12 longitudinally in parallel with the camshaft 12. The controlshaft 17 is rotated and controlled by an actuator 18 including anelectric motor. The actuator 18 is driven and controlled by a controlunit 19.

As illustrated in FIGS. 2 and 3, the control shaft 17 includes: one sideshaft portion 20 with a predetermined diameter at a front end portionthereof; the other side shaft portion 21 with the same diameter as thatof the one side shaft portion 20 at a rear end portion thereof; and acircular eccentric shaft portion 22 arranged between the one side shaftportion 20 and the other side shaft portion 21, having a larger diameterthan that of the one side shaft portion 20 and the other side shaftportion 21, with its shaft center decentered by a predeterminedeccentric amount (offset) “e” from the one side shaft portion 20 and theother side shaft portion 21. The one side shaft portion 20, the otherside shaft portion 21, and the circular eccentric shaft portion 22 areintegrally connected.

More specifically, a shaft center O2 of the eccentric shaft portion 22is set eccentrically so as to be decentered radially by an eccentricamount “e” from a shaft center O1 of the one side shaft portion 20 andthe other side shaft portion 21, and the eccentric shaft portion 22 iseccentrically rotated around the shaft center O1 of the one side shaftportion 20 and the other side shaft portion 21.

The control shaft 17 is mounted with a rocking cam 23 in a swingablematter so as to be capable of lifting the engine valve 2.

The rocking cam 23 includes one side rocking cam member 23A attached tothe one side shaft portion 20 and the other side rocking cam member 23Battached to the other side shaft portion 21.

The one side rocking cam member 23A includes one side base circleportion 24A which prevents the one side engine valve 2A from beinglifted; and one side cam portion 25A which is projected radially fromthe one side base circle portion 24A and causes the one side enginevalve 2A to be lifted.

As illustrated in FIG. 2, one side hollow portion 26A having an internaldiameter larger than a diameter of the one side shaft portion 20 isformed on an inner circumferential surface of the one side base circleportion 24A, and one side internal gear piece 27A as a spur gear isformed on an inner circumferential surface of the one side hollowportion 26A. The center of the one side base circle portion 24A iscoaxially aligned with that of the one side shaft portion 20.

Furthermore, one side support portion 29A having one side shaft hole 28Athrough which the one side shaft portion 20 passes is projected axiallyand continuously connected to an outer end portion of the one side basecircle portion 24A. More specifically, the one side rocking cam member23A includes the one side base circle portion 24A which prevents a liftof a cam portion 15 of a rotating cam 13 of the camshaft 12 from beingtransmitted to the one side roller finger follower 5A, and the one sidecam portion 25A which causes a lift of the cam portion 15 of therotating cam 13 of the camshaft 12 to be transmitted to the one sideroller finger follower 5A.

It is further to be noted that the center of the one side base circleportion 24A is coaxially aligned with that of the one side shaft portion20 of the control shaft 17. Therefore, when the control shaft 17 isrotated, the control shaft 17 does not press or move the one side rollerfinger follower 5A.

The other side rocking cam member 23B includes the other side basecircle portion 24B which prevents the other side engine valve 2B frombeing lifted, and the other side cam portion 25B which is projectedradially from the other side base circle portion 24B and causes theother side engine valve 2B to be lifted.

As illustrated in FIG. 2, the other side hollow portion 26B having aninternal diameter larger than the diameter of the other side shaftportion 21 is formed on an inner circumferential surface of the otherside base circle portion 24B, and the other side internal gear piece 27Bas a spur gear is formed on an inner circumferential surface of theother side hollow portion 26B. The center of the other side base circleportion 24B is coaxially aligned with that of the other side shaftportion 21.

Furthermore, the other side support portion 29B having the other sideshaft hole 28B through which the other side shaft portion 21 passes isprojected radially and continuously connected to an outer end portion ofthe other side base circle portion 24B.

More specifically, the other side rocking cam member 23B includes theother side base circle portion 24B which prevents a lift of the camportion 15 of the rotating cam 13 of the camshaft 12 from beingtransmitted to the other side roller finger follower 5B, and the otherside cam portion 25B which causes a lift of the cam portion 15 of therotating cam 13 of the camshaft 12 to be transmitted to the other sideroller finger follower 5B.

It is further to be noted that the center of the other side base circleportion 24B is coaxially aligned with that of the other side shaftportion 21 of the control shaft 17. Therefore, when the control shaft 17is rotated, the control shaft 17 does not press or move the other sideroller finger follower 5B.

In the above structure, the one side base circle portion 24A and theother side base circle portion 24B constitute a base circle portion 24of the rocking cam 23. The one side cam portion 25A and the other sidecam portion 25B constitute a cam portion 25 of the rocking cam 23. Theone side hollow portion 26A and the other side hollow portion 26Bconstitute a hollow portion 26 of the rocking cam 23. The one sideinternal gear piece 27A and the other side internal gear piece 27Bconstitute an internal gear piece 27 of the rocking cam 23.

A cam follower (rocker arm) 31 is coupled to the rocking cam 23 throughthe position changing mechanism 30. The cam follower 31 is rocked by therotating cam 13 of the camshaft 12 and causes the rocking cam 23 to berocked.

The cam follower 31 includes: a tubular body 33 having a shaft throughhole 32 into which the eccentric shaft portion 22 of the control shaft17 is fitted; a pair of roller support portions 34 and 34 projectedtoward the camshaft side in an axial center position of the tubular body33; a roller pin 35 supported on the pair of roller support portions 34and 34; and a roller 36 rotatably supported on the roller pin 35 betweenthe pair of roller support portions 34 and 34.

The cam follower 31 is swingably supported on the eccentric shaftportion 22.

As illustrated in FIGS. 2 and 3, the tubular body 33 includes one sideexternal gear piece 37A which is formed in a front end portion thereofas a spur gear engaged with one side internal gear piece 27A of the oneside rocking cam member 23A with the eccentric shaft portion 22 as therotating shaft, and the other side external gear piece 37B which isformed in a rear end portion thereof as a spur gear engaged with theother side internal gear piece 27B of the other side rocking cam 23Bwith the eccentric shaft portion 22 as the rotating shaft.

The one side external gear piece 37A and the other side external gearpiece 37B constitute an external gear 37 of the cam follower 31.

Further, the one side external gear piece 37A, the other side externalgear piece 37B, and the eccentric shaft portion 22 are arranged insidethe one side hollow portion 26A and the other side hollow portion 26B,respectively. Thus, the axial length of the eccentric shaft portion 22can be shortened and mountability of the variable valve operating system16 on the internal combustion engine 1 can be improved.

As illustrated in FIG. 3, the axial centers of the shaft of the one sideexternal gear piece 37A and the other side external gear piece 37B arecoaxially aligned with the rocking center of the cam follower 31.Further, the axial centers of the shaft of the one side internal gearpiece 27A and the other side internal gear piece 27B are coaxiallyaligned with the rocking center of the rocking cam 23. Thus, the oneside internal gear piece 27A and the other side internal gear piece 27Bare engaged with the one side external gear piece 37A and the other sideexternal gear piece 37B offset by an eccentric amount “e”.

In the present embodiment, the position changing mechanism 30 isconfigured as a cycloid mechanism including the eccentric shaft portion22, the one side internal gear piece 27A, the other side internal gearpiece 27B, the one side external gear piece 37A, and the other sideexternal gear piece 37B. The position changing mechanism 30 changes liftcharacteristics of the one side engine valve 2A and the other sideengine valve 2B by changing a relative positional relationship of theone and the other side rocking cam members 23A and 23B with respect tothe cam follower 31.

As illustrated in FIG. 3, the one side and the other side internal gearpieces 27A and 27B of the one side and the other side rocking cammembers 23A and 23B are engaged with the one and the other side externalgear pieces 37A and 37B of the tubular body 33 of the cam follower 31,respectively, in an eccentric direction of the eccentric shaft portion22. Thus, each number of teeth of the one and the other side internalgear pieces 27A and 27B, and each number of the one and the other sideexternal gear pieces 37A 37B are determined, respectively, by theeccentric amount “e”.

Further, it is to be noted that the one side rocking cam member 23A andthe other side rocking cam member 23B are attached to the front endportion and the rear end portion of the tubular body 33 of the camfollower 31, respectively. Therefore, two valves 2A and 2B can be drivenby one cam follower 31.

The variable valve operating system 16 according to the presentembodiment has a structure in which the control shaft 17, the camfollower 31, and the rocking cam 23 are additionally arranged to aconventional roller rocker valve train system between the camshaft 12and the roller finger follower 5.

As illustrated in FIGS. 4 and 5, the lift amount of the engine valve 2is continuously changed by changing a nip angle (β) between the camfollower 31 and the rocking cam 23 by a rotational angle (α) of thecontrol shaft 17.

Further, as illustrated in FIG. 3, the variable valve operating system16 operates the engine valve 2 by causing the rocking cam 23 to pressand move the roller finger follower 5, but the roller finger follower 5may be replaced with a tappet or the like to be applicable to variousvalve train systems.

The variable valve operating system 16 operates as follows. When theopening/closing characteristics of the engine valve 2 are changed, thecontrol shaft 17 is rotated to thereby revolve the external gear 37around the axial center of the control shaft by the eccentric shaftportion 22. This revolving motion of the external gear 37 causes anengagement point “G” (see FIGS. 4 and 5) of the internal gear 27 withrespect to the external gear 37 to be moved in a circumferentialdirection of the internal gear 27, and the position of the rocking cam23 with respect to the cam follower 31 is then changed by the movementof the engagement point “G” of the internal gear 27.

As described above, the position changing mechanism 30 is constructed asa cycloid mechanism including the eccentric shaft portion 22 of thecontrol shaft 17, the external gear 37 of the cam follower 31, and theinternal gear 27 of the rocking cam 23, and the position changingmechanism 30 operates such that the position of the rocking cam 23 withrespect to the cam follower 31 is changed by the rotation of the controlshaft 17 to thereby change the lift characteristics of the engine valve2. According to the position changing mechanism 30 of the structurementioned above, the lift characteristics of the engine valve 2 are notaffected by a relative thermal expansion difference between the controlshaft 17 and the internal combustion engine 1.

Furthermore, the position changing mechanism 30 is configured by theexternal gear 37 and the internal gear 27 made of a spur gear which canbe easily manufactured in comparison with a conventional helical spline,thus simplifying the structure and improving the productivity of thevariable valve operating system 16.

Further, when the control shaft 17 is rotated, the cam follower 31 movessuch that a contact point thereof to the rotating cam 13 moves along anouter circumference of the rotary cam 13, and the lift amount of theengine valve 2 is changed by the movement of the rocking cam 23. Whenthe control shaft 17 is rotated in a direction to reduce the lift amountof the engine valve 2, the contact point between the cam follower 31 andthe rotating cam 13 moves in a direction opposite to the rotatingdirection of the rotating cam 13 (toward an advance angle side).According to such movement, as the lift amount of the engine valve 2 isreduced, the cam timing of closing the engine valve 2 can be advancedand pumping loss can be reduced.

Next, a lifting operation of the variable valve operating system 16 willbe described with reference to FIGS. 4 and 5.

As illustrated in FIG. 4A, in order to reduce the lift amount when theengine valve 2 is not operated, the control shaft 17 is rotatedcounterclockwise. At this time, the angle of the rotated control shaft17 with respect to a reference position is assumed to be α1. Morespecifically, the rotation of the eccentric shaft portion 22 causes theexternal gear 37 to be revolved counterclockwise around the shaft centerO1 of the one side shaft portion 20 and the other side shaft portion 21.Then, the nip angle between the cam follower 31 and the rocking cam 23is decreased to β1 and the contact position between the rotating cam 13and the cam follower 31 is moved in an advance angle direction to γ1. Atthis time, even if the cam portion 15 of the rotating cam 13 contactsthe roller 36 to swing the rocking cam 23, as illustrated in FIG. 4B,the rocking cam 23 and the roller 8 of the roller finger follower 5contact to each other through the base circle portion 24. Therefore, theengine valve 2 is scarcely lifted, and the lift amount is minimized(small lift condition) (see R1 in FIG. 6).

Meanwhile, as illustrated in FIG. 5A, in order to increase the liftamount when the engine valve 2 is not operated, the control shaft 17 isrotated clockwise until the angle with respect to the reference positionis changed from an angle of al to an angle of α2. Then, the externalgear 37 is rotated clockwise around the shaft center O2 of the eccentricshaft portion 22. Then, the position changing mechanism 30 operating asa cycloid mechanism causes the cam follower 31 to slide rightward(illustrated by an arrow M in FIG. 5A) until the contact positionbetween the rotating cam 13 and the cam follower 31 is changed from γ1to γ2. Thus, the valve timing retards. At the same time, the rocking cam23 is rotated clockwise (in a valve opening direction) around the shaftcenter O1 of the one and the other side shaft portions 20 and 21 untilthe nip angle between the cam follower 31 and the rocking cam 23 isincreased from β1 to β2.

At this time, the nip angle is β2>β1, and as illustrated in FIG. 5B,when the engine valve 2 is operated, the contact range between therocking cam 23 and the roller finger follower 5 via the cam portion 25is increased. Thus, the roller finger follower 5 is greatly swung aroundthe top spherical portion of the hydraulic lash adjuster 11, and theengine valve 2 is greatly operated (i.e., a large lift condition) (seeR2 in FIG. 6).

Further, as illustrated in FIG. 6, in a relationship between the liftamount of the engine valve 2 and the opening/closing timing, the smallerthe lift amount, the more the maximum lift position (top portion of thelift curve) moves in an advance angle direction.

This is because when the lift amount of the engine valve 2 is reduced,the contact position between the cam follower 31 and the rotating cam 13moves in a direction (advance angle direction) opposite to the rotatingdirection of the rotating cam 13, and thus, the opening/closing timingof the engine valve 2 is sped up. Accordingly, when the engine valve 2is under a small lift condition, the engine valve 2 can be controlled tobe quickly closed, thereby reducing the pumping loss and improving fuelconsumption efficiency.

Furthermore, unlike the conventional system, since there is no need foraxial control of the control shaft, a stable accuracy or performance canbe obtained even under a small lift condition without being affected bya thermal expansion coefficient of the material constituting the partsor components of the engine due to temperature change.

The use of the position changing mechanism 30 as a cycloid mechanism inthe present embodiment provides the following advantages.

According to the reduction principle of the cycloid mechanism, adeflection angle of α>a deflection angle of β. More specifically, interm of the rotation of the control shaft 17 to the rotation of therocking cam 23, equation (α2-α1)>β2-β1) is obtained, and thus, a largedeceleration is enabled, and in the meantime, in term of the torquetransmission, the control shaft 17 on the acceleration side is notsusceptible to torque variation. In other word, this leads toimprovement of reliability of the actuator 18 for driving the controlshaft 17.

Furthermore, since the internal gear 27 of the rocking cam 23 and theexternal gear 37 of the cam follower 31 are in a relationship betweenthe external gear and the internal gear, a large contact ratio (toothsurface contact ratio) can be ensured and the slip ratio can be reduced,thus advantageously improving the reliability of the tooth surface.

Still furthermore, since the eccentric amount “e” of the rotating shaftsof the internal gear 27 and the external gear 37 is generally verysmall, even when the rotating cam 13 is operated, both gears have a verysmall amount of slip, thus advantageously improving the reliability ofthe tooth surface.

It is further to be noted that the present invention is not limited tothe described embodiment and many other changes and modifications may bemade without departing from the scopes of the appended claims.

For example, in the described embodiment, although two external gearsare attached to one cam follower and two valves are driven by one camportion, the present invention may be configured to provide two camportions and two cam followers.

Furthermore, in the described embodiment, although a valve train systemusing a roller finger follower (RFF) is used as an example, the presentinvention may be applied to a direct acting valve train system using atappet or the like.

The variable valve operating system according to the present inventioncan be applied to an internal combustion engine of various vehicles.

1. A variable valve operating system for an internal combustion engineincluding an engine valve and a cam shaft operating the engine valve,the variable valve operating system comprising: a rocking cam, whichlifts the engine valve, supported to a control shaft to be swingable; acam follower rocking the rocking cam; and a position changing mechanismwhich couples the cam follower with the rocking cam, the positionchanging mechanism being configured to change a relative positionalrelationship of the rocking cam with respect to the cam follower tothereby change lift characteristics of the engine valve, the positionchanging mechanism comprising: a circular eccentric portion which isformed to the control shaft in a manner decentered from an axis of thecontrol shaft; an external gear formed on the cam follower swingablysupported on the eccentric shaft portion with the eccentric shaftportion as the rotating shaft; and an internal gear formed on therocking cam with the control shaft as the rotating shaft so as to beengaged with the external gear, wherein the control shaft is rotatedwhen opening/closing characteristics of the engine valve are changed,the external gear is revolved by the eccentric shaft portion around theaxis of the control shaft, an engaged portion of the internal gear withthe external gear is moved in a circumferential direction of theinternal gear by the revolution of the external gear, and the positionof the rocking cam with respect to the cam follower is changed by themovement of the engaged portion of the internal gear.
 2. The variablevalve operating system for an internal combustion engine according toclaim 1, wherein when the control shaft is rotated, the cam followermoves such that a contact point to the rotating cam moves along an outercircumference of the rotating cam and the movement of the rocking camcauses a lift amount of the engine valve to be changed, and when thecontrol shaft is rotated in a direction to reduce the lift amount of theengine valve, the contact point between the cam follower and therotating cam moves in a direction opposite to the rotating direction ofthe rotating cam.
 3. The variable valve operating system for an internalcombustion engine according to claim 1, wherein the rocking cam includesa base circle portion which prevents the engine valve from being liftedand a cam portion which is projected radially from the base circleportion, a hollow portion is formed on an inner circumference of thebase portion, the internal gear is formed on an inner circumferencesurface of the hollow portion, and the external gear and the eccentricshaft portion are arranged inside the hollow portion.